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Now in 993 land ...
 
aigel's Avatar
 
Join Date: Mar 2003
Location: L.A.-> SF Bay Area
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real gem for your horror picture collectors and some reading too!

http://www.bushwacker-racing.com/blowup/blowup.html

Anyone willing to guess what went wrong? Sounds like it just came unglued at 8k rpm, no shifts, leave alone a missed one.

Here the writeup how it was built:

http://www.bushwacker-racing.com/phase11/3.4Lmotor.htm

Not much detail on parts, tolerances etc. Did the shop have Waynes' book? "They havn't worked on Porsche engines before but to them, it's just an air-pump." = That may as well be part of the problem?

I am no machinist, but my backwoods crank grinder in Bayouland had a nicer equipped machine shop than these folks. And he ground cranks mainly for industrial mechanics (compressors, tractors, generators ...), not for NASCAR.

I am more than curious to hear what you guys have to say! I hope to learn something!

George

Edit: PS: And a history of the slippery slope that's real cool:
http://www.bushwacker-racing.com/build-it.htm#phase0
From the first upgrades for a time trial to the diehard 40 foot motorhome! Glad that I'd run out of cash earlier!
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Last edited by aigel; 08-11-2004 at 12:07 AM..
Old 08-10-2004, 11:48 PM
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john walker's workshop's Avatar
 
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could have broken a valve spring, a valve then hit the piston, breaking the head off, which broke the piston, and then the rod took out everything else.
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Old 08-11-2004, 08:31 AM
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OK, here is my diagnosis (just a guess because there is lots of other I would like to see):

Spring bind. The first clue is the failure of the rocker-to-cam surface. The rocker is under extreme duress when the cam is trying to open the valve and it wonít open any farther. Another clue is the comment about aluminum valve spring retainers. With the spring(s) bound solid, the retainers are taking the full force.

The aluminum retainers probably bent first so the engine would turn over on the stand. There must have been only very minimal bind or the builder couldnít have timed the cams. Since the valve springs were always at, or just short of bind, this caused some springs to break. Any spring bind is disastrous.

I think the chain ramp damage is from the incredible forces necessary turn the engine over through spring bind. It also can be as a result of the failure. Were both sides damaged?

Of course once there was a broken spring, the keepers and retainer came off. This allowed the valve to drop into the cylinder and all hell broke loose. Everything appears to be the usual carnage except I have never seen a piston turned over.

The additional things I would want to see are to look at the spring installation on the other cylinders. How close is it to spring bind? I would want to see how many spring shims were used on the #3 valve that failed compared to all the other valves. The builder could have simply misread the gauge or miscounted shims.

Another issue is the contact of valves-to-pistons on the earlier engine. I would want to know the initial clearance, which cylinders, and the clearance after the failure. This might be related to the failure. It might be a separate issue that hadnít caused a failure Ė yet.

I can think of several other possible scenarios: Valves hitting the piston and initiating the failure sequence is the next most likely. His site postings arenít exactly clear.


I donít think this failure had anything to do with it being a racing engine. This is an example of the degree of care that must go into a modified engine. If you stuck a vacuum gauge in this guyís ear, it would peg the meter.


Another interesting point is to look at the degree of effort and expense that went into the unusual bore/stroke. A custom ground crankshaft. Custom rod bearings. Custom rod length and big-end diameter. I assume stock P&C but how did they determine deck and valve clearances? Well Ö maybe not.
I think single plug was mandated by the rules. Look how far the plug is from center with that 102 mm diameter. That combustion chamber is screaming for a second plug.


Thanks for posting this. While none of us like to see broken Porsche stuff, it is very instructive. I have always helped others solve their problems so I didnít repeat them.


Best,
Grady
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Old 08-11-2004, 10:08 AM
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I race with this guy and he said the aluminum retainer failed. He was trying to put more hours on it than the aluminum retainers can take.

-Andy
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Old 08-11-2004, 04:42 PM
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I bet the valve spring broke first.
The engine had 200 hours on it? Or did this guy have a blow-up at the end of 2002,(Laguna Seca) and then another blown engine June 2003 (Fontana)?
I would never ever use aluminum retainers in a 911.

I have only heard good things about Valley balancing. But I did not know they were building/machining 911's.
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Old 08-13-2004, 12:30 PM
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Now in 993 land ...
 
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Yeah, I think you guys mix up the engine he blew in 2002 vs. the new one in 2003. The new one was not high mileage and should not have come apart like that.

George
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Old 08-13-2004, 12:41 PM
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